Methods and graphics processing units for determining differential data for rays of a ray bundle

A graphics processing unit configured to process rays in a ray bundle, the graphics processing unit comprising processing logic configured utilize data determined by executing an instance of a shader program corresponding to a first ray of the ray bundle in the execution of an instance of the shader program for a further ray of the ray bundle.

A non-transitory computer readable storage medium having stored thereon computer readable instructions that, when executed at a computer system, cause the computer system to perform a method of processing rays in a ray bundle in a graphics processing system, the method comprising using data determined by executing an instance of a shader program corresponding to a first ray of the ray bundle in the execution of an instance of the shader program for a further ray of the ray bundle.